Questions and Exercises: Threads - Java Tutorial 5.0 英文版

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Trail: Essential Java Classes
Lesson: Threads: Doing Two or More Tasks at Once

Questions and Exercises: Threads

Questions

What method in Timer or TimerTask can you use to determine when the task was most recently scheduled to execute? (Hint: You can find the answer by looking at the API documentation for Timer and TimerTask. Remember that these classes were introduced in version 1.3 of the Java platform.)

What is the effect on a Thread object of calling the start method?

What are the two ways you can provide the implementation for a thread's run method?

Exercises

Convert AnnoyingBeep.java so that the initial delay is 5 seconds instead of 0.

Convert AnnoyingBeep.java to use the scheduleAtFixedRate method instead of schedule to schedule the task. Change the implementation of the run method so that if it is called too late for a warning beep (say, more than 5 milliseconds after it was scheduled to run), nothing happens — no beep and string are generated. (Hint: Remember your answer to question 1.)

Change the main program of TwoThreadsTest.java so that it creates a third thread named "Bora Bora". Compile and run the program again. Note that you will also need SimpleThread.java. Does this change your vacation destination?

Compile and run RaceTest.java and SelfishRunner.java on your computer. Do you have a time-sliced system?

Well-behaved threads voluntarily relinquish the CPU periodically and give other threads an opportunity to run. Rewrite the SelfishRunner class to be a PoliteRunner. Be sure to modify the main program in RaceTest.java to create PoliteRunners instead of SelfishRunners.

Check your answers.

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